Overwintering adult Spotted wing Drosophila (SWD) can live for months. Dr. Jennifer Forman Orth of the Massachusetts Department of Agricultural Resources (MDAR) talked about SWD during the Invasive Insect Certification Program for Landscape, Nursery, and Urban Forest Pests provided by UMass Extension.
SWD are thought to have arrived in New England by Hurricane Irene back in 2011. As they prefer soft fruit, that’s not good news for blueberry growers, or other fruit growers as they will also attack cherries. Unlike other fruit/vinegar flies which only attack rotting or overripe fruit, they attack ripe fruit as females can cut into ripening fruit with a saw-like edge on their ovipositor (egg-laying appendage).
SWD eat the fruits of everything from dogwood to climbing nightshade, American pokeberries (pokeweed), strawberries, elderberries, currants, apples, Asian plums, tomatoes, plums and plumcots and Asian pear. The adult flies lay eggs on the fruit and when the eggs hatch, the worm-like larvae crawl into the fruit.
SWD is small and can be a challenge to identify, but the males have obvious dark spots on the ends of their wings. There can be multiple generations laying eggs in one season. Adults live 20 to 30 days, laying 350 eggs in a lifetime which take 12 to 72 hours to hatch. After three days, the larva forms a pupa inside or outside of the fruit for four to 15 days, and then adults emerge. Their ability to overwinter extends their life.
If someone is concerned about SWD, MDAR recommends putting a monitoring program in place. “A cup trap is probably your best option,” said Forman Orth. Put an apple cider mix or yeast and sugar mix into a cup topped with 40 or so 1/8 inch holes poked near the top, and hang it two to three feet above the ground to attract SWD. A sticky card also works. Fruit can be dunked in a salt-water mix to check for the presence of larvae.
Cultural controls include clearing out overripe fruit and disposing of it in a plastic bag to avoid spreading it; do not add it to compost. Netting can be used, but “if you are not absolutely sure your crop is free of SWD, don’t net.” Harvest early and often.
If using pesticides, apply to adult stage SWD. Use short residual pesticides if necessary to allow for harvesting of fruit. The short lifecycle of SWD plus overlapping generations make the timing of spraying difficult. Spinosad, malathion, pyrethroids and neonicotinoids are effective but may require multiple sprayings near harvest time. “There are lots of issues with ending up with pesticide resistance. If you’re going organic, spinifex is effective. Check labels carefully, and make sure the product you are looking into is labeled for application to fruit.” Use each product on a two-week alternating rotation to avoid building pesticide resistance in SWD. When using insecticides, be sure to thoroughly read and follow all label instructions. Some active ingredients, depending on the formulation or individual product, cannot be used in food crops. Look to your local Extension program for more information about safe use of insecticides.
Her next insect, the Asian Tiger Mosquito (ATM) is not a plant pest. “If working outside, it might affect you in the future,” said Forman Orth. It can be spread through tire recycling because stagnant water held in dark, sun-absorbing tires creates a perfect breeding site. ATM only needs enough water as contained in a bottle cap to breed in. It is an aggressive day biter versus other mosquitoes which feed at dawn, dusk, and at night.
“The reason we care is that ATM can carry the Zika virus, Dengue fever, Eastern equine encephalitis, West Nile virus, and Chikungunya virus. Though note that the current outbreak of Zika virus is being caused by a different mosquito species that we do not have in Massachusetts,” said Forman Orth.
At ¼ inch long, ATM is smaller than other mosquitos. It is black with white stripes running down the center of its head and thorax, and white stripes on its legs. Even with those seemingly striking characteristics, however, the Asian Tiger Mosquito is very difficult to identify.
It was first found in Texas 1985, then in Florida in 1997. Originally thought to be unable to overwinter in Massachusetts, it has moved north and is thought to have become established in New Bedford, and has recently expanded to surrounding towns including Dartmouth. While repeated finds of a single mosquito have occurred in other cities and towns in Massachusetts, including Worcester, Boston, and Ayer, nothing in those areas has become established.
MDAR is working with regional mosquito control projects and the Department of Public Health to reach out to businesses and the public to educate them about not leaving standing water in containers long enough to become mosquito breeding sites, and with tire recycling facilities to reduce its spread from known sites.
Don’t leave any containers, large or small, where they can collect standing water. If that does happen, tip out the water at least once a week.